This invention relates to a heat exchanger for a Stirling engine.
FIG. 1 illustrates a conventional heat exchanger for a Stirling engine which was disclosed in Japanese Laid-Open Patent Application No. 52-25952. In the figure, element number 1 is a high-temperature cylinder, element number 1a is an expansion space which is defined by the top portion of the high-temperature cylinder 1, element number 2 is a cylindrical regenerator housing which concentrically surrounds the high-temperature cylinder 1 and is secured thereto at its upper end, and element number 3 is a low-temperature cylinder which is secured to the regenerator housing 2 by securing bolts 102. A hermetic seal is formed between the high-temperature cylinder 1 and the low temperature cylinder 3 by an O-ring seal 3b. Element number 3a is a compression space which is defined by the bottom portion of the high-temperature cylinder 1 and the top portion of the low-temperature cylinder 3. Elements number 4 are a plurality of heater tubes which extend outwards from the head of the high-temperature cylinder 1 and which connect to the head portion of the regenerator housing 2. Element number 5 is a cylindrical regenerator which is made of a wire mesh or the like and which is disposed inside the regenerator housing, concentrically surrounding the high-temperature cylinder 1. Element number 6 is a cylindrical cooler which is disposed below the regenerator 5 and which concentrically surrounds the lower portion of the high-temperature cylinder 1. Element number 6a is one of a number of axially-extending cooling pipes which form part of the cooler 6 and which are connected thereto by soldering or other means. Elements numbers 6b and 6c are O-ring seals which form a hermetic seal between the cooler 6 and the regenerator housing 2. Elements numbers 7 and 8 are respectively a cooling water intake pipe and a cooling water discharge pipe through which cooling water passes for the cooler 6. Element number 9 is a displacer having a hollow, sealed center, and element number 10 is a gas seal ring which is mounted on the displacer 9 and forms a seal between the displacer 9 and the inner surface of the high-temperature cylinder 1. Element number 101 is a rod seal which is provided in the central shaft portion of a power piston 11 and which forms a seal between the power piston 11 and a displacer rod 13 which passes through the center of the power piston 11 and is connected to the displacer 9. Element number 12 is a gas seal ring which is mounted on the outside of the power piston 11 and forms a seal between it and the inner surface of the low-temperature cylinder 3. Element number 14 is a power piston rod which is secured to the power piston 11. The bottom portion of the low-temperature cylinder 3 serves as a crankcase. The crankcase is equipped with a crank mechanism and connecting rods which reciprocate the displacer 9 and the power piston 11 with a prescribed phase difference.
In a Stirling engine of this type, by continuously heating and cooling the heater tubes 4 and the cooler 6, respectively, a working fluid is expanded and compressed, and the working fluid flows back and forth inside the heat exchanger. Namely, the working fluid flows from the heater tubes 4 to the cooler 6 through the regenerator 5 or in the opposite direction. The thermal energy which is transferred to the heater tubes 4 is converted into the rotational energy of a crankshaft through the reciprocation of the piston 11 and the displacer 9.
A conventional heat exchanger of the type illustrated in FIG. 1 has a number of problems. First, as the high-temperature cylinder 1 and the regenerator housing 2 must be able to withstand an internal pressure of approximately 10-60 atmospheres, their walls must be made very thick. As a result, the thermal conduction losses from the high-temperature cylinder 1 to the cooler 6 through the regenerator housing 2 are large, and the thermal efficiency of the engine ends up being poor. Furthermore, at the portion where the high-temperature cylinder 1 is connected to the regenerator housing 2, there is an abrupt change in cross-sectional area. As a result, large concentrations of welding stresses and thermal stresses can develop at this portion, and damage due to high stresses can easily occur.